Fibrinogen is required for blood clot or thrombus formation as activation of the coagulation pathways converts soluble fibrinogen to insoluble fibrin. The lysis of a clot or thrombus generates fibrin(ogen) degradation products (FDPs/fdps). FDPs/fdps are generated in conditions such as disseminated intravascular coagulation (DIC) and during thrombolytic therapy. The role of any specific low molecular weight FDPs/fdps (<5000 daltons) in causing the diffuse vascular injury of multi-organ system failure and platelet dysfunction in DIC has not been characterized. During thrombolytic therapy for acute myocardial infarction, the level of FDPs/fdps correlate with the bleeding complication. Similarly, no specific FDPs/fdps (<5000 daltons) have been identified that cause platelet dysfunction during thrombolytic therapy. Recently we have shown that beta 15-42, a fdp that has been detected to circulate in vivo by cleavage of fibrinogen with thrombin and plasmin, causes platelet dysfunction and cytotoxic effect on cultured endothelial cells in vitro. In this proposal we will further characterize the mechanism of platelet and endothelial cell dysfunction induced by one fdp, beta 15-42, in vitro using biochemical techniques of affinity chromatography, chemical heterobifunctional cross-linker, and equilibrium dialysis. Structure-function analysis of beta 15-42 using synthetic peptides with deletions, substitutions, or additions of amino acids will be studied. Once the mechanism of platelet and endothelial dysfunction induced by beta 15-42 is defined, potential therapeutic modalities will be studied in vitro. The applicant, a board-certified Hematologist, has received an excellent clinical and bench research training in Hematology at the University of Washington in Seattle. He has been a student of endothelial cell--platelet biology. This proposal is an outgrowth of his own independent thinking. This research proposal will be carried out in the laboratory of Dr. Jan McDonagh, Beth Israel Hospital, Boston. Dr. McDonagh has an extensive research background in thrombosis and hemostasis. A key research interest of hers is fibrinogen and FDPs/fdps. The sponsor and the environment in the Longwood Medical Area should be a fertile ground for Dr. Chen to develop into an independent investigator.